Logic Circuits
- Logic gates can be combined to produce different outputs
- The combination of two or more logic gates forms a logic circuit
- A logic diagram is a visual representation of combinations of logic gates within a logic circuit
An example of Logic Circuit
- In this diagram, the inputs are represented by A and B
- P is the output of the OR gate on the left and becomes the input of the NOT gate. This is called an intermediary output
- Q is the final output of the logic circuit
Exam Tip
- You may be asked to draw a logic circuit from a logic statement or a boolean expression. Circuits must be drawn without simplification
- Logic circuits will be limited to a maximum of three inputs and one output
An example of Logic Circuit
- This logic circuit contains three inputs (A, B and C)
- It contains a NAND gate, a NOT gate, a NOR gate and finally an OR gate
- X is the final output
- This logic circuit can be represented as a logic expression as
X=((NOT(A NAND B) OR (B NOR C
Worked example
A sprinkler system switches on if it is not daytime (input A) and the temperature is greater than 40 (input B)
Draw a logic circuit to represent the problem statement above
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Exam Tip
- You may need to draw a logic circuit from a problem statement (as in the example above), from a truth table or from a boolean expression
